Commuter trains east of Sac (to Rocklin or Auburn, though I suspect Lincoln might be another good terminal) and west to Dixon have been in regional transportation plan wish lists for years. The money to add 1 or 2 tracks to UP for the purpose hasn't been, and for now doesn't seem likely to be found. Given how things have been working in the commute train biz lately (viz. Caltrain?) we might see HSR before commute trains in Sac, and if light rail makes it to Roseville first (it'll go to the airport and Elk Grove first of course) they might never happen. In the great scheme of funding programs, though, light rail may have more chance of actually happening than commuter trains that require major upgrades/additions to UP.

The market might be there. If you're catching the 0740 Amtrak to Oakland in Sac, stand back when the train arrives (it's the one from Auburn): plenty of commuters getting off and they're in a hurry! Roseville and Placer County Transit both have fairly active commute bus routes too.